Ion exchange active fluoropolymer films have been widely used in industry, particularly as ion exchange membranes in chlor-alkali cells. Such membranes are made from fluorinated polymers having ion exchange active groups attached to pendant groups from the polymeric backbone.
It has been found that ion exchange membranes frequently operate more efficiently if their surface is roughened. This is especially true when such membranes are used in processes where a gas is generated adjacent to the membrane. Roughened membranes release the gas from its surface and does not result in gas blinding of the membrane. However, the preparation of such roughened membrane surfaces is difficult. A simple method for producing roughened membranes would be highly desirable.
It has also been found than ion exchange membranes frequently operate more efficiently if the surface is roughened or has electrically inactive particles embedded into its surface. Such particles also cause gas bubbles to be released from the surface of the membrane. However, prior art method for producing such membranes is not entirely satisfactory because such membranes require specialized materials and additional process steps to the finished membrane.
U.S. Pat. No. 4,457,815 discloses a permionic membrane having a porous film or surface and electrocatalyst on at least one surface thereof. Also disclosed in an electrolytic cell with the permionic membrane, an electrolytic process utilizing the permionic membrane, and an electrolytic process utilizing electrolytic cell.
U.S. Pat. No. 4,349,422 discloses a process and cell for electrolysis of alkali metal halides, especially sodium chloride, wherein the anolyte and the catholyte compartments are separated by a fluorinated ion exchange membrane whose surface facing the catholyte compartment is of a polymer having carboxylic functionality and which has a roughened surface which does not excell 1.5 microns. Such a cell and process operate at high current efficiency, low voltage and low power consumption.
U.S. Pat. No. 4,468,301 discloses a process for the electrolysis of an aqueous alkali metal chloride in a cell which comprises an anode and a cathode which are partitioned by an ion exchange membrane having at least one roughened surface. The electrodes are spaced apart in non-contacting relationship from the membrane surface up to a distance of no more than 2 millimeters.
European Patent Application No. 0,122,049 discloses an unreinforced ion exchange membrane which comprises fluorinated polymer which has carboxylic functional groups, which has a hydrogen bubble release layer on the cathode side thereof, and which has channels open to the outer surface of the anode-facing side thereof. Precursor membrane, which may contain partially embedded sacrificial members, and from which the unreinforced ion exchange membrane is made, is also disclosed. The unreinforced ion exchange membrane can be used to separate the compartments of a chlor-alkali cell, and such a cell operates at low voltage, high current efficiency, and low power consumption.
A method for quickly and easily manufacturing ion exchange membranes having a bubble release layer would be highly desirable. It is the purpose of this invention to provide such a method.